JPH0455773B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a low-pressure casting method for light alloy castings, and more particularly, the present invention relates to a method for low-pressure casting of light alloy castings, and more particularly, a mold is constructed from mold materials having different thermal conductivities, and a cavity defined in the mold is used. By directing the solidification of the molten metal filled in the mold in a predetermined direction due to the difference in thermal conductivity of the mold materials, it is possible to obtain a high-quality cast product without casting defects. The present invention relates to a low-pressure casting method for light alloy castings that makes it possible to improve production efficiency by shortening one working cycle of the casting process. [Background of the Invention] In general, low-pressure casting methods are widely used, for example, when mass producing automobile parts and the like. In this low-pressure casting method, a molten metal made of a light alloy such as an aluminum alloy is placed in a sealed container, the surface of the molten metal is pressurized with relatively low-pressure gas, usually compressed air, and the molten metal is passed through a hot water supply pipe into a mold. This is a method of manufacturing a cast product by filling a cavity corresponding to the product defined therein. Therefore, a schematic configuration of a low-pressure casting apparatus generally used in the low-pressure casting method is illustrated in FIG. 1. In FIG. 1, a casting apparatus 2 basically comprises a casting mold 3 and a hot water supply section 4. As shown in FIG. The casting mold 3 is composed of an upper mold 5, a lower mold 6, and horizontal molds 7a and 7b that are fitted to the upper mold 5 and the lower mold 6, and these upper mold 5, lower mold 6, and horizontal mold 7a ,7
A cavity 8 corresponding to the product shape is defined by b. In this case, the lower die 6 is installed on a fixed die base 9, and the lower die 6 is provided with a sprue 10, and the upper die 5 is attached to a movable die base 12 that can be vertically displaced by a pressure cylinder 11. On the other hand, the horizontal types 7a and 7b have cylinders 13a,
13b are connected, and the horizontal molds 7a, 7b are movable in the horizontal direction when the molds are opened under the action of the cylinders 13a, 13b. A crucible 15 for storing molten metal is installed in a heat-retaining furnace 14 as a closed container constituting the hot water supply section 4, and a heater 1 for heat-retaining is installed around the outer periphery of the crucible 15.
6 is provided. Further, a hot water supply pipe 17 is inserted into the crucible 15, and the end of this hot water supply pipe 17 is connected to the sprue 10. Furthermore, a compressed air supply and exhaust pipe 18 is arranged in the heat retention furnace 14 . In the above configuration, the compressed air supply and exhaust pipe 1
When compressed air at a predetermined pressure is fed into the heat-retaining furnace 14 through 8, the surface of the molten metal stored in the crucible 15 is pressurized, and the molten metal passes through the hot water supply pipe 17 and is drawn into the casting mold 3 from the sprue 10. It is injected into the cavity 8 that has been formed. Next, after filling the cavity 8 with molten metal and maintaining it at a predetermined pressure, the compressed air in the heat insulating furnace 14 is extracted through the compressed air supply and exhaust pipe 18, and the molten metal filled in the cavity is cooled and solidified for a predetermined period of time. . A cast product having a predetermined shape can be obtained in one working cycle of such a casting process (see FIG. 2). In such a low-pressure casting method, in order to cast a high-quality product with a good structure without casting defects, the molten metal filled in the cavity must solidify rapidly, and the molten metal must flow inside the cavity. Solidification progresses gradually from the end toward the sprue. It is necessary to perform so-called directional coagulation.
The reason for this is that casting defects such as cavities are removed from the structure of the cast product by performing the directional solidification as described above. Conventionally, in low-pressure casting methods, various methods have been attempted to control the mold temperature in order to effect directional solidification of the molten metal filled into the cavity. However, the mold temperature fluctuates periodically within one work cycle of the casting process as shown in FIG. In addition, since mold materials generally use materials such as steel with low thermal conductivity, they have poor responsiveness to temperature adjustment, which makes temperature control for directional solidification extremely difficult. It was not possible to carry out effective control. Therefore, conventionally, the above-mentioned one work cycle was appropriately adjusted, the pressurization time of the molten metal fed into the cavity was lengthened so that the mold temperature was within a predetermined temperature range, and then the molten metal was solidified for a relatively long time. Casting defects are prevented by allowing the process to progress naturally within the mold. However, in reality, for example, casting defects such as cavities are likely to occur in relatively thick parts of the product.
Furthermore, it has been pointed out that there is a problem in that the casting efficiency is not improved to a certain extent because one work cycle becomes that long. [Object of the Invention] The present invention has been made to overcome the above-mentioned disadvantages, and includes forming a cavity corresponding to a product using several types of members having different thermal conductivities, and injecting molten metal into the cavity. After pouring the molten metal, the difference in thermal conductivity of each member is used to promote directional solidification of the molten metal in a predetermined direction, thereby casting a high-quality product with a good structure without casting defects. It is possible to do this, and one of the casting processes is
The object of the present invention is to provide a low-pressure casting method for light alloy castings that can shorten the work cycle and further improve production efficiency. [Means for Achieving the Object] In order to achieve the above-mentioned object, the present invention pressurizes the surface of the molten metal stored in a closed container under the pressure of a fluid, and transfers the molten metal from a sprue to a mold through a hot water supply pipe. In a low pressure casting method for filling a cavity defined within the mold, comprising the mold and defining a sprue;
Directing the mold from a lower mold made of a metal member with low thermal conductivity to a sliding mold made of a metal member with higher thermal conductivity than the lower mold, and further to an upper mold made of a metal member with higher thermal conductivity than the sliding mold. The method is characterized in that a cavity is filled with molten metal, and the solidification time of the molten metal is regulated based on the difference in thermal conductivity between the lower mold, the sliding mold, and the upper mold to obtain a cast product. [Embodiments] Next, preferred embodiments of the low-pressure casting method for light alloy castings according to the present invention in relation to the apparatus for carrying out the method will be listed and explained in detail below with reference to the accompanying drawings. . In FIG. 3, reference numeral 20 indicates the casting apparatus body. A casting mold 22 constituting the casting device main body 20 is arranged so as to be slidably fitted into a lower mold 24, an upper mold 26 disposed above the lower mold 24, and the lower mold 24 and the upper mold 26. The upper mold 26, the lower mold 24, and the sliding molds 28a, 28b, 30a, 30b define a cavity 32. be done. In this case, the cavity 32 has a shape suitable for casting a cylinder head constituting an internal combustion engine of an automobile or the like. In addition, as described later, the lower mold 24,
Upper mold 26 and sliding molds 28a, 28b, 30a,
30b are formed using different types of metal materials having different thermal conductivities. Therefore, a stepped hole 34 is formed at a predetermined portion of the lower die 24, and a nozzle 36 having a sprue 35 communicating with the cavity 32 is fitted into the stepped hole 34. A stalk 38 for feeding the molten metal is connected to the nozzle 36, and the stalk 38 is fitted into a crucible (not shown) that is installed below the lower die 24 and stores the molten metal. Furthermore, a passage 40 for introducing a cooling fluid is defined inside the lower mold 24 . In this case, the passage 4
0 extends into the insert 42 installed in the lower mold 24. On the other hand, the upper die 26 is attached to a die base 44 which is connected to an actuator including a cylinder (not shown) and is movable in the vertical direction. This die base 4
A cooling block 46 is interposed between the mold 4 and the upper mold 26, and a passage 48 for introducing cooling fluid is formed in the cooling block 46. moreover,
As can be understood from the figure, a chiller 50a, 50b
is the hole 52 that passes through the die base 44 and the upper die 26.
a, 52b. Said chiller 50a, 5
Inside 0b is a passage 5 filled with cooling fluid.
4a and 54b are formed. Further, after opening the mold, an extrusion pin 55 for taking out the cast product is connected to the die base 44, the cooling block 46, and the upper mold 2.
6 is inserted into the hole 56 passing through the hole 56. This extrusion pin 55 has its proximal end attached to the mounting member 57, and its distal end faces the cavity 32. Next, sliding molds 28a and 28b and sliding molds 30a,
30b is fitted. These sliding molds 28a, 28b
and 30a, 30b are connecting members 58a, 5, respectively.
It is connected to an actuator such as a cylinder (not shown) via 8b and 60a, 60b. Also,
The sliding molds 28a, 28b and 30a, 30b
Holes 62a, 62b and 64a, 64b for gas venting communicating with the cavity 32 are formed in the holes 62a, 62b and 64.
Passages 66 and 68 are formed through which cooling fluid flows in a direction perpendicular to a and 64b. In addition, in the figure, reference numerals 70a to 70f indicate sand cores, among which sand cores 70b and 70c form an intake passage and an exhaust passage of the cylinder head,
In addition, the sand core 70a and the sand cores 70d to 70
f is for forming a water jacket through which cooling water flows. Next, the casting mold 22 configured as above
A low-pressure casting method for light alloy castings according to the present invention using the method will be described. First, it is assumed that the various molds constituting the casting mold 22 used in the low-pressure casting method of the present invention are made of the materials shown in Table 1.

[Table] Therefore, the sand cores 70a to 70f are placed at predetermined positions within the cavity 32 defined within the casting mold 22. In this case, the sand cores 70a to 70f are made of, for example, resin coated sand, which is molded using a predetermined mold. Next, by driving a cylinder or the like (not shown), the upper mold 26 and the sliding molds 28a, 2
8b, 30a, and 30b are moved close to the lower mold 24 to perform mold clamping. Next, the cavity 32 is filled with molten aluminum alloy from the sprue 35 formed in the nozzle 36 via the stalk 38 . In this case, the casting conditions are an aluminum alloy molten metal temperature of 680° C., a pressing force of 0.28 Kg/cm ² and a casting cycle of 3 minutes, which corresponds to JIS AC2B. In other words, the temperature of the molten aluminum alloy stored in a crucible (not shown) is set to 680℃.
By keeping the surface of the molten metal under pressure with compressed air, the molten metal is passed through the stalk 38 to the sprue
Fill the cavity 32 with 0.28Kg/
Pressurize with a pressure of cm ² . Therefore, after maintaining the above state for a predetermined period of time,
Compressed air is removed to solidify the molten metal filled in the cavity 32. As shown in Table 1, the lower mold 24, the upper mold 26, and the sliding molds 28a, 28b and 30a, 30b are constructed using materials having different thermal conductivities. In this case, the lower die 24 is made of carbon tool steel material with the lowest thermal conductivity. Therefore, when the high temperature molten metal stored in the cavity 32 solidifies and contracts, the cavity 3
Cooling is suppressed so that the portion of the cavity 32 facing the lower mold 24 will finally solidify so that molten metal can be replenished into the mold 2 from the sprue 35. On the other hand, sliding type 2
8a, 28b and the sliding molds 30, 30b are made of beryllium bronze material having higher thermal conductivity than the lower mold 24, and the upper mold 26 is made of the sliding molds 28a, 28b and 30a, 30b. A chromium-copper alloy material is used, which has a higher thermal conductivity. For this reason, heat dissipation of the molten metal filled into the cavity 32 is promoted or delayed due to the difference in thermal conductivity, and as a result, from the upper mold 26, sliding molds 28a, 28b, and 30a, 30b to the lower mold 24. Coagulation progresses in this order in a directional manner, achieving so-called directional coagulation. Therefore, it is possible to avoid casting defects such as cavities from occurring in the structure of the cast product, and it is possible to obtain a high-quality cast product with a healthy structure. Also, a cooling block 46, sliding molds 28a, 28b, 30a, 3 interposed in the upper mold 26,
0b and a passageway 48 formed in the lower die 24,
If cooling water is introduced into 66, 68, and 40 as necessary, the cooling of the molten metal in the cavity 32 is further promoted, and as a result, the casting cycle time is shortened and efficient casting can be performed. It becomes possible. In fact, in this embodiment, one casting cycle is
The results show that the process can be carried out in minutes, which is about half the time compared to conventional methods. [Effects of the Invention] As described above, according to the present invention, materials with different thermal conductivities are used for the various molds constituting the mold, and by utilizing the difference in thermal conductivity, Directional solidification is promoted so that the solidification of the molten metal filling the cavity proceeds in a predetermined direction. For this reason, the molten metal filled into the cavity solidifies sequentially as it heads toward the sprue.
The advantage is that casting defects such as cavities can be avoided, and a cast product with a sound structure and excellent quality can be obtained. Furthermore, as a result of using a material with high thermal conductivity, solidification itself progresses quickly, resulting in the effect of shortening the casting cycle and further improving the manufacturing efficiency of cast products. Therefore, the present invention has the effect that the incidence of defective products as a whole is low, high quality cast products can be manufactured, and productivity can be significantly improved. Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to these embodiments, and various improvements and changes in design are possible without departing from the gist of the present invention. Of course.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing a schematic configuration of a low-pressure casting device according to the prior art, FIG. 2 is a graph explaining an example of a conventional casting cycle, and FIG. 3 is a low-pressure light alloy casting according to the present invention. FIG. 2 is a schematic vertical cross-sectional view of a low-pressure casting device used in the casting method. 20... Casting device main body, 22... Casting mold,
24...Lower mold, 26...Upper mold, 28a, 28b,
30a, 30b...Sliding type, 32...Cavity, 35...Gate, 38...Stoke, 46...
Cooling block, 50a, 50b... chiller.

Claims (1)

[Claims] 1. Low-pressure casting for pressurizing the surface of molten metal stored in a closed container under the pressure of a fluid and filling the molten metal from a sprue into a cavity defined in a mold through a hot water supply pipe. configuring the mold and defining a sprue;
Directing the mold from a lower mold made of a metal member with low thermal conductivity to a sliding mold made of a metal member with higher thermal conductivity than the lower mold, and further to an upper mold made of a metal member with higher thermal conductivity than the sliding mold. A low-pressure casting method for light alloy castings, characterized in that a cavity is filled with molten metal, and the solidification time of the molten metal is regulated based on the difference in thermal conductivity between the lower mold, the sliding mold, and the upper mold to obtain a cast product.